1. Field of the Invention
The present invention relates to a silicone rubber composition that comprises an organopolysiloxane and undergoes curing via an addition reaction to generate a silicone rubber, and more specifically, relates to an addition curable liquid silicone rubber composition which, even when used to produce cured molded products by injection molding, generates no burrs on the molded product, as well as a method of regulating the fluidity of such a composition, and a method of injection molding a silicone rubber composition.
2. Description of the Prior Art
Silicone rubbers exhibit excellent levels of heat resistance and cold resistance, and superior electrical properties and the like, and are consequently used as rubber molded products in a wide variety of applications. In recent years, a method known as burr-free or runnerless molding has become increasingly widespread in the injection molding of addition curable liquid silicone rubbers. This is a molding method in which no wasted cured product is produced, and in which secondary processing is unnecessary, namely, a method in which no sprue or runners exist (or even if they do exist, the liquid silicone rubber does not cure), meaning the generation of burrs is minimized. This molding method has significant benefits, including enabling automation of the injection molding, shortening of the molding cycle, and a reduction in the cost of the molded products. With this molding method, in addition to the required mechanical specifications such as the precision of the mold construction and the mold parting surface, and the precision with which the injection molding device measures and discharges the rubber composition, a rubber material that is resistant to burr generation must also be used.
The rubber material injected into the cavity undergoes a reduction in viscosity under high shear velocity, and can then flow into gaps within the mold and generate burrs on curing. One technique for preventing the generation of these burrs is a method in which the viscosity of the rubber material is increased. However in injection molding, a material pump is usually used to supply the rubber material to the injection unit of the injection molding device, and if the viscosity of the rubber material is high, then a practical problem arises in that the supply process using the material pump takes considerable time.